This application claims the priority of Japanese application number 08-347103, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to an apparatus for controlling the oil pressure in an automatic transmission of a vehicle when changing a transmission speed (a gear ratio), and more particularly to a control apparatus and a method for engaging and disengaging a clutch by directly and electrically controlling the oil pressure acting on the clutch (friction coupling device).
An apparatus disclosed in Japanese Patent Application Un-examined laid-open No. JP-A-63-263248 is a widely known example of apparatus for engaging and disengaging the clutch by electrically controlling the clutch operating oil pressure. This Japanese Patent Unexamined Publication described a system in which when controlling the oil pressure acting on the disengaging clutch to change the transmission speed, the revolution speed of the transmission input shaft (turbine revolution speed) is controlled to follow up the preset target value of the revolution speed of the transmission input shaft. This invention proposes a method for performing stable control of the disengaging clutch, realized by feedback control of the operating oil pressure of the disengaging clutch according to the change in the input shaft revolution speed which changes with the engaging state of the engaging clutch.
According to the above-mentioned well-known example, the operating oil pressure of the disengaging clutch is controlled by feedback of the transmission input shaft revolution speed. However, there is a difficulty in discriminating between the change in the input shaft revolution speed caused by an increase of the engine torque due to pressing down on the accelerator pedal, and the change of the input shaft revolution speed attending on the disengagement of the disengaging clutch. This difficulty results in the degradation of the controllability of the operating oil pressure control. Accordingly, a great shock at gear change is inevitable, which arises from a shift in disengaging timing of the disengaging clutch when changing the gears.